From 60a4cf8ec5c93104d3cfb9fc5a5bac8fb18cc8e4 Mon Sep 17 00:00:00 2001
From: Farid Zakaria <fmzakari@google.com>
Date: Thu, 13 Aug 2020 12:48:15 -0700
Subject: [PATCH] Prefer local nix-index if present

The nix-index database offered in the derivation
may be more out of date than what is present on the
system.

In fact, prefer any local nix-index database to the prebuilt
database included with comma
---
 ,           |  9 ++++++++-
 .gitignore  |  2 ++
 default.nix | 19 +++++++++----------
 3 files changed, 19 insertions(+), 11 deletions(-)
 create mode 100644 .gitignore

diff --git a/, b/,
index 875fa30..c67b254 100755
--- a/,
+++ b/,
@@ -18,6 +18,13 @@ else
   install=""
 fi
 
+# if a nix-index exists locally; use that as it's likely much more recent
+# than the prebuilt one.
+database=$PREBUILT_NIX_INDEX_DB
+if [ -f "${HOME}/.cache/nix-index/files" ]; then
+    database="${HOME}/.cache/nix-index"
+fi
+
 argv0=$1; shift
 
 case "${argv0}" in
@@ -25,7 +32,7 @@ case "${argv0}" in
     attr="${argv0}"
     ;;
   *)
-    attr="$(nix-locate --db "${NIX_INDEX_DB}" --top-level --minimal --at-root --whole-name "/bin/${argv0}")"
+    attr="$(nix-locate --db "${database}" --top-level --minimal --at-root --whole-name "/bin/${argv0}")"
     if [[ "$(echo "${attr}" | wc -l)" -ne 1 ]]; then
       attr="$(echo "${attr}" | fzy)"
     fi
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..cf07729
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+# ignore nix-build result folter
+result
diff --git a/default.nix b/default.nix
index fc391b3..611e4ea 100644
--- a/default.nix
+++ b/default.nix
@@ -8,6 +8,7 @@
 , fzy ? pkgs.fzy
 , makeWrapper ? pkgs.makeWrapper
 , runCommand ? pkgs.runCommand
+, linkFarm ? pkgs.linkFarm
 
 # We use this to add matchers for stuff that's not in upstream nixpkgs, but is
 # in our own overlay. No fuzzy matching from multiple options here, it's just:
@@ -27,19 +28,17 @@ let
 
   # nix-locate needs the --db argument to be a directory containing a file
   # named "files".
-  nixIndexDB = runCommand "nix-index-cache" {} ''
-    mkdir $out
-    ln -s ${indexCache.out} $out/files
-  '';
+  nixIndexDB = linkFarm "nix-index-cache" [
+    { name = "files"; path = indexCache; }
+  ];
 
 in
-
 stdenv.mkDerivation rec {
   name = "comma";
 
   src = ./.;
 
-  buildInputs = [ nix-index.out nix.out fzy.out ];
+  buildInputs = [ nix-index nix fzy ];
   nativeBuildInputs = [ makeWrapper ];
 
   installPhase = let
@@ -49,10 +48,10 @@ stdenv.mkDerivation rec {
     sed -e 's/@OVERLAY_PACKAGES@/${caseCondition}/' < , > $out/bin/,
     chmod +x $out/bin/,
     wrapProgram $out/bin/, \
-      --set NIX_INDEX_DB ${nixIndexDB.out} \
-      --prefix PATH : ${nix-index.out}/bin \
-      --prefix PATH : ${nix.out}/bin \
-      --prefix PATH : ${fzy.out}/bin
+      --set PREBUILT_NIX_INDEX_DB ${nixIndexDB} \
+      --prefix PATH : ${nix-index}/bin \
+      --prefix PATH : ${nix}/bin \
+      --prefix PATH : ${fzy}/bin
 
     ln -s $out/bin/, $out/bin/comma
   '';